Chronotype and depressive symptoms in students: An investigation of possible mechanisms

Figures & data

Table 1. Characteristics of the sample (N = 742).

Characteristic	M(SD) or n (%)
Age, years, M(SD)	21.4(2.9)
Gender, female, n (%)	553 (74.5)
Education
Lower college, n (%)	18 (2.4)
Higher college, n (%)	169 (24.8)
University, n (%)	555 (74.8)
Chronotype (MEQ score), M(SD)	46.6 (10.0)
Depressive symptoms (QIDS-SR score), M(SD)	6.0 (4.4)
Sleep quality (PSQI score), M(SD)	5.5 (2.6)
Number of alcoholic beverages per week, M(SD)	5.5 (6.6)
Milligram of consumed caffeine per week, M(SD)	567 (670)
Smoking, n (%)	161 (21.7)
Cannabis, n (%)	37 (5.0)
Cognitive emotion regulation strategies (CERQ)
Self-blame, M(SD)	9.9 (3.2)
Acceptance, M(SD)	12.2 (3.2)
Rumination, M(SD)	11.2 (3.8)
Positive refocusing, M(SD)	10.6 (3.4)
Refocus on planning, M(SD)	13.5 (3.3)
Positive reappraisal, M(SD)	12.8 (3.6)
Putting into perspective, M(SD)	12.1 (3.7)
Catastrophizing, M(SD)	6.2 (2.6)
Blaming others, M(SD)	6.2 (2.3)
Behavioral inhibition (BIS) M(SD)	14.3 (4.2)
Behavioral activation (BAS)
Drive, M(SD)	8.8 (2.2)
Fun seeking, M(SD)	8.5 (2.1)
Reward responsiveness, M(SD)	8.7 (2.0)

MEQ: Morningness Eveningness Questionnaire; QIDS-SR: Quick Inventory of Depressive Symptomatology – Self-Rated; PSQI: Pittsburgh Sleep Quality Index; CERQ: Cognitive Emotion Regulation Questionnaire; BIS: Behavioral Inhibition Scale; BAS: Behavioral Activation Scale.

Table 2. Summary of statistical mediation analyses between chronotype (IV) and depressive symptoms (DV) in the cross-sectional sample.

		Effect of IV on M (a)		Effect of M on DV (b)		Total effect of IV on DV (c)		Direct effect of IV on DV (c′)
Model	Mediator	Effect (SE)	p	Effect (SE)	p	Effect (SE)	p	Effect (SE)	p	Unstandardized indirect effect of IV on DV (a × b) (SE)	95% confidence interval (a × b)
1 (n = 742)	Sleep quality (PSQI)	−0.051 (0.010)	<0.0001	0.909 (0.052)	<0.0001	−0.036 (0.016)	0.028	0.010 (0.014)	0.476	−0.046 (0.01)	−0.067 to −0.027
2 (n = 733)	Alcohol	−0.148 (0.023)	<0.0001	−0.084 (0.027)	0.002	−0.035 (0.017)	0.033	−0.042 (0.017)	0.013	0.012 (0.004)	0.005–0.022
	Caffeine	−4.23 (2.52)	0.094	−0.0003 (0.0002)	0.301	−0.035 (0.017)	0.033	−0.042 (0.017)	0.013	0.001 (0.002)	−0.001–0.006
	Smoking	−0.286 (0.077)	<0.001	0.023 (0.008)	0.006	−0.035 (0.017)	0.033	−0.042 (0.017)	0.013	−0.006 (0.003)	−0.014 to −0.002
	Cannabis	−0.066 (0.059)	0.260	0.001 (0.010)	0.907	−0.035 (0.017)	0.033	−0.042 (0.017)	0.013	−0.0001 (0.002)	−0.004–0.002
3 (n = 702)	Self-blame	−0.027 (0.013)	0.034	0.425 (0.051)	<0.0001	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.012 (0.006)	−0.023 to −0.001
	Acceptance	−0.013 (0.012)	0.303	0.081 (0.052)	0.117	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.001 (0.001)	−0.005–0.0007
	Rumination	−0.003 (0.015)	0.833	0.102 (0.046)	0.026	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.0003 (0.002)	−0.004–0.003
	Positive refocusing	0.010 (0.013)	0.448	−0.065 (0.049)	0.188	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.0006 (0.001)	−0.005–0.0008
	Refocus on planning	0.028 (0.013)	0.029	−0.128 (0.055)	0.019	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.004 (0.002)	−0.010 to −0.0003
	Positive reappraisal	0.048 (0.014)	0.0005	−0.118 (0.059)	0.044	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.006 (0.003)	−0.015 to −0.0008
	Putting into perspective	−0.004 (0.014)	0.769	−0.060 (0.049)	0.222	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	0.0002 (0.001)	−0.001–0.004
	Catastrophizing	−0.014 (0.010)	0.152	0.379 (0.064)	<0.0001	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.005 (0.004)	−0.015–0.002
	Blaming others	−0.018 (0.009)	0.040	0.008 (0.070)	0.906	−0.033 (0.017)	0.053	−0.005 (0.015)	0.760	−0.0001 (0.001)	−0.003–0.003
4 (n = 683)	Behavioral inhibition	0.001 (0.015)	0.933	0.401 (0.042)	<0.0001	−0.037 (0.017)	0.031	−0.036 (0.016)	0.025	0.0005 (0.007)	−0.013–0.013
	Drive	0.005 (0.008)	0.581	0.157 (0.088)	0.074	−0.037 (0.017)	0.031	−0.036 (0.016)	0.025	0.0007 (0.002)	−0.002–0.006
	Fun seeking	−0.019 (0.008)	0.019	0.098 (0.089)	0.274	−0.037 (0.017)	0.031	−0.036 (0.016)	0.025	−0.002 (0.002)	−0.008–0.001
	Reward responsiveness	0.0000 (0.008)	0.996	−0.370 (0.093)	0.0001	−0.037 (0.017)	0.031	−0.036 (0.016)	0.025	0.0000 (0.003)	−0.006–0.006

IV: Independent variable (chronotype; lower scores indicate eveningness); DV: dependent variable (depressive symptoms; higher scores indicated more depressive symptoms); PSQI: Pittsburgh Sleep Quality Index.

Note: All analyses are adjusted for age and gender. Significant mediation effects are indicated in bold.

Table 3. Results of final mediation model (n = 702).

	Effect of IV on M (a)		Effect of M on DV (b)		Total effect of IV on DV (c)		Direct effect of IV on DV (c′)
Mediator	Effect (SE)	p	Effect (SE)	p	Effect (SE)	p	Effect (SE)	p	Unstandardized indirect effect of IV on DV (a × b) (SE)	95% confidence interval (a × b)
Sleep quality (PSQI)	−0.048 (0.010)	<0.0001	0.765 (0.050)	<0.0001	−0.033 (0.017)	0.0529	0.019 (0.014)	0.154	−0.037 (0.009)	−0.056 to −0.021
Alcohol	−0.143 (0.024)	<0.0001	−0.050 (0.022)	0.021	−0.033 (0.017)	0.0529	0.019 (0.014)	0.154	0.007 (0.003)	0.002–0.015
Smoking	−0.279 (0.078)	0.0004	0.009 (0.007)	0.147	−0.033 (0.017)	0.0529	0.019 (0.014)	0.154	−0.003 (0.002)	−0.008–0.001
Self-blame	−0.027 (0.013)	0.034	0.428 (0.041)	<0.0001	−0.033 (0.017)	0.0529	0.019 (0.014)	0.154	−0.012 (0.006)	−0.023 to −0.001
Refocus on planning	0.028 (0.013)	0.029	−0.074 (0.048)	0.120	−0.033 (0.017)	0.0529	0.019 (0.014)	0.154	−0.002 (0.002)	−.007–0.000
Positive reappraisal	0.048 (0.014)	0.0005	−0.121 (0.043)	0.005	−0.033 (0.017)	0.0529	0.019 (0.014)	0.154	−0.006 (0.003)	−0.013 to −0.002

IV: Independent variable (chronotype; lower scores indicate eveningness); DV: dependent variable (depressive symptoms). Note: All analyses are adjusted for age and gender.

PSQI: Pittsburgh Sleep Quality Index.

Significant mediation effects are indicated in bold.

Figure 1. Means and standard errors on depressive symptoms and total sleep quality stratified by chronotype in the cross-sectional sample (N = 742).